lower unit/ impeller gasket seals

[cam1399]

Hey had a question about impeller seals. I noticed a little water in my oil. I have a 1984 mercury 150 black max. Im wanting to change the impeller and gaskets. I noticed o rings in the kit. How does the base come off under the rubber impeller? Are there seals and o rings under that? Also the prop seal. I got the tool to loosen the big ring out. Is it just that one seal by the shaft?

 

[Faztbullet]

2 seals on prop shaft, 2 seals on water pump 1 o-ring

 

[Chris1956]

You will want to pressure test the gearcase to determine what is leaking. You can use a bicycle pump and the tube from the lube pump to do that.

Often the shift shaft seal leaks.

 

[cam1399]

Will do. How is that one changed?

 

[Chris1956]

The shift shaft bushing with the seal should unscrew from the gearcase. I ground down a 1/2" black pipe connector into a spanner to unscrew the bushing, but you can unscrew it with a punch as well.

Test the gearcase with a few PSI of air pressure and some soapy water to determine where the leak is.

 

[cam1399]

Okay good deal. Do I have to worry about the shift shaft coming out?

 

[Chris1956]

Not normally. I would not yank on it though.

The shift seals are avail at a lot of places like Amazon as well as boat motor parts places.

 

[cam1399]

I bought a lower unit seal kit and an impeller kit. Will they come with everything?

 

[Chris1956]

You will need to look at the seal kit. Usually the shift seal is an aluminum bushing, with an oring inside it and a gasket on the fitting above the threads.

The prop shaft seals are a PIA to install. With any luck you will not need to replace them. The waterpump base driveshaft seal often leaks as well. That is pretty easy to replace.

 

[cam1399]

Thanks. I’ve done an impeller but noting more on a mercury. Will drop it today.

 

[Chris1956]

If the waterpump cover ss liner is scratched, replace it. If the water pump base is scratched (it is melted) and should be replaced as well. If reusing the pump base, be careful to replace the water pump base driveshaft seal. In either case, sand the driveshaft to make is clean and smooth, and lubricate both the seal and driveshaft with oil or grease, before installing the pump base.